Usually, blow-molded containers are transported by the neck in a row along a feeding rail, where they slide freely by gravity or in which they are forced to move by a compressed air stream.
Before they are gripped by a starwheel in order to be moved to a filling unit at a predetermined rate, the containers must be spaced apart at a predetermined pitch. This is why there is generally provided a transfer wheel connecting the feed rail to the starwheel. The transfer wheel comprises, at its periphery, a plurality of recesses equally spaced apart. Each recess engages a container at a loading point located at an end of the feeding rail, and releases it at an unloading point located at a periphery of the starwheel. Containers follow an arc-of-circle path from the loading point to the unloading point.
Such a structure is disclosed in Italian patent application IT 1 260 380 (Parmatec). One can also refer to US patent application No. 2003/0106779 (Stocchi) and to U.S. Pat. No. 6,591,967 (Doudement).
During the transfer, containers are subjected to acceleration and deceleration forces, both tangential and radial. As the containers are suspended by their necks, such forces may cause container misalignment, thereby resulting in wrong positioning of the containers on the starwheel and possibly causing damages to the filling machine.
In order to prevent such damages, a classical solution consists in providing the machine with means for sensing wrong positioning and means for ejecting wrongly positioned containers from the starwheel.
As long as machine safety is the only concern, such a solution is unquestionably efficient. However, it is complex to set up and does not prevent reduction of production rates.